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S E Simopoulos - One of the best experts on this subject based on the ideXlab platform.

  • radiological characteristics and investigation of the Radioactive Equilibrium in the ashes produced in lignite fired power plants
    Journal of Environmental Radioactivity, 2004
    Co-Authors: D J Karangelos, M.j. Anagnostakis, N P Petropoulos, E P Hinis, S E Simopoulos
    Abstract:

    Coal- and lignite-fired power plants produce significant amounts of ashes, which are quite often being used as additives in cement and other building materials. In many cases, coal and lignite present high concentrations of naturally occurring radionuclides, such as 238U, 226Ra, 210Pb, 232Th and 40K. During the combustion process, the produced ashes are enriched in the above radionuclides. The different enrichment of the various radionuclides within a Radioactive series, such as that of 238U, results in the disturbance of Radioactive secular Equilibrium. An extensive research project for the determination of the natural radioactivity of lignite and ashes from Greek lignite-fired power plants is in progress in the Nuclear Engineering Department of the National Technical University of Athens (NED-NTUA) since 1983. This paper presents detailed results for the natural radioactivity, the secular Radioactive Equilibrium disturbance and the radon exhalation rate of the fly-ash collected at the different stages along the emission control system of a lignite-fired power plant as well as of the bottom-ash. From the results obtained so far, it may be concluded that 226Ra radioactivity of fly-ash in some cases exceeds 1 kBq kg−1, which is much higher than the mean 226Ra radioactivity of surface soils in Greece (25 Bq kg−1). Furthermore, the radioactivity of 210Pb in fly-ash may reach 4 kBq kg−1. These results are interpreted in relation to the physical properties of the investigated nuclides, the temperature in the flue-gas pathway, as well as the fly-ash grain size distribution. It is concluded that towards the coldest parts of the emission control system of the power plant, the radioactivity of some natural nuclides is gradually enhanced, secular Radioactive Equilibrium is significantly disturbed and the radon exhalation rate tends to increase.

  • determination of depleted uranium in environmental samples by gamma spectroscopic techniques
    Journal of Environmental Radioactivity, 2004
    Co-Authors: D J Karangelos, M.j. Anagnostakis, E P Hinis, S E Simopoulos, Zora S Zunic
    Abstract:

    sequently for the isotopic abundance of the uranium isotopes in the sample. 235U is determined from the analysis of the multiplet photopeak at 186 keV. DU may be detected with this technique provided that the 238U activity of the DU is higher than ~20% of that of 238 U in the natural uranium of the sample. The analyses by NES-NTUA of surface soil samples collected well before the dispersion of depleted uranium in Kosovo, made evident that Kosovo is an area of high natural background, with a pronounced surface soil variation in natural uranium content, and 238U activity reaching values as high as 330 Bqkg -1 . It was also observed that disturbance of Radioactive Equilibrium among the nuclides of the uranium series is quite often observed due to leaching and weathering, with the ratio of the activities of 238 U and 226 Ra ranging from 0.17 to 5.5. After the military operations in Kosovo, surface soil and vegetation samples as well as DU penetrators were analysed in NES-NTUA. Among the soil samples analysed it was found that some of those collected around a DU penetrator crater were contaminated by DU, with 238 U activity exceeding 2 kBqkg -1 , and ratio of 238 U/ 226 Ra exceeding the value of 10. In these soil samples, the natural isotopic abundance of the uranium isotopes was significantly disrupted; this allowed for an estimation of the isotopic abundance of 235U in the dispersed DU of about 0.2%, which agrees very well with relevant values found in the literature for DU penetrators. DU in the vegetation samples analysed was below detection limit. The analysis of DU penetrators led to the detection 238U, 235 U and their daughters, and to an estimation of the dose-rate due to the gamma-rays emitted from the penetrator, which reached 6.5 µSvh-1 on the surface, sloping to background at the distance of about 40 cm.

  • photon attenuation natural radioactivity content and radon exhalation rate of building materials
    Journal of Environmental Radioactivity, 2002
    Co-Authors: N P Petropoulos, M.j. Anagnostakis, S E Simopoulos
    Abstract:

    Abstract High concentrations of natural radionuclides in building materials can result in high dose rates indoors, from both internal and external exposure. In dose calculations, the main radionuclides of interest are 226 Ra, 232 Th and 40 K. Usually much attention is paid to 226 Ra due to 222 Rn exhalation and the subsequent internal exposure. Other radionuclides of the uranium series such as 238 U and 210 Pb, emitting low energy photons are not usually determined and an assumption of Radioactive Equilibrium is made. The above assumption is seldom checked mainly because of the difficulties in the γ-spectroscopic analysis of low energy photons. For the determination of radionuclides emitting low-energy photons, in samples like building materials where intense self-absorption of the photons exists, a method for self-absorption correction has been developed. The method needs as input the linear attenuation coefficient μ for the material under analysis. This paper presents: 1. Correlations in the form μ = f ( ρ , E ) developed for the estimation of the linear attenuation coefficient μ (cm −1 ), as a function of the material packing density ρ (g cm −3 ) and the photon energy E (keV), for building materials as well as other materials of environmental importance. 2. Gamma-spectroscopic analysis techniques used for the determination of 238 U, 226 Ra, 210 Pb, 232 Th and 40 K in environmental samples, together with the results obtained from the analysis of building materials used in Greece, and industrial by-products used for the production of building materials. Among the techniques used, one is based on the direct determination of 226 Ra and 235 U from the analysis of the multiplet photopeak at ∼186 keV. 3. Results from radon exhalation measurements of building materials such as cement and fly-ash and building structures conducted in the radon chambers in our Laboratory. Based on the above results, dosimetric calculations are also reported.

L E Thomas - One of the best experts on this subject based on the ideXlab platform.

  • quantitation of protactinium 231pa in abyssal carbonate
    Journal of Analytical Atomic Spectrometry, 2012
    Co-Authors: Peter Van Calsteren, L E Thomas
    Abstract:

    Quantitation of protactinium, 231Pa in abyssal carbonates at ∼10−12 g g−1 levels, presents certain challenges because it is the only isotope of this element that is present in the natural environment and its half-life of 32800 y is too long for useful measurement using alpha-particle or gamma-ray spectroscopy. However, because it is an isotope in the 235U decay chain, closely linked to the 238U decay chain, quantitation can be achieved relative to a carbonate standard in secular Radioactive Equilibrium. The 238U, 235U, 234U, 230Th and 232Th isotopes in the carbonate standard are determined with a mixed 236U–229Th spike using isotope dilution protocols and a Multi-Collector Inductively Coupled Plasma Mass Spectrometer.

  • quantitation of protactinium 231 pa in abyssal carbonate
    2012
    Co-Authors: Peter Van Calsteren, L E Thomas
    Abstract:

    Quantitation of protactinium, 231 Pa in abyssal carbonates at ~10 –12 g g –1 levels, presents certain challenges because it is the only isotope of this element that is present in the natural environment and its half-life of 32 800 y is too long for useful measurement using alpha-particle or gamma-ray spectroscopy. However, because it is an isotope in the 235 U decay chain, closely linked to the 238 U decay chain, quantitation can be achieved relative to a carbonate standard in secular Radioactive Equilibrium. The 238 U, 235 U, 234 U, 230 Th and 232 Th isotopes in the carbonate standard are determined with a mixed 236 U- 229 Th spike using isotope dilution protocols and a Multi-Collector Inductively Coupled Plasma Mass Spectrometer.

M.j. Anagnostakis - One of the best experts on this subject based on the ideXlab platform.

  • environmental radioactivity measurements and applications difficulties current status and future trends
    Radiation Physics and Chemistry, 2015
    Co-Authors: M.j. Anagnostakis
    Abstract:

    For several decades natural and artificial radioactivity in the environment have been extensively studied all around the world. Nuclear accidents – mainly that of Chernobyl – have led to the development of the field of radioecology, while detector systems and techniques – with predominant that of γ-spectrometry – have been continuously developed through the years to meet researchers' needs. The study of natural radionuclides that was originally limited to 226Ra, 232Th and 40K was then extended to include radionuclides such as 234Th, 210Pb, 235U and 7Be, which allowed the study of Radioactive Equilibrium. Besides their importance from the radiation protection point of view, many radionuclides are also used as tracers of environmental processes, such as aerosol and transportation of air masses studies (7Be, 10Be, 22Na), soil erosion, sedimentation and geochronology (210Pb, 137Cs), marine ecosystems studies and studies related to climate change. All these studies require specialized samplings strategies and sampling preparation techniques as well as high quality measurements, while the improvement of detection limits is often of vital importance. This work is a review of environmental radioactivity measurements and applications, mainly focused in the field of γ-spectrometry, for which difficulties and limitations will be presented, together with future trends, new challenges and applications.

  • radiological characteristics and investigation of the Radioactive Equilibrium in the ashes produced in lignite fired power plants
    Journal of Environmental Radioactivity, 2004
    Co-Authors: D J Karangelos, M.j. Anagnostakis, N P Petropoulos, E P Hinis, S E Simopoulos
    Abstract:

    Coal- and lignite-fired power plants produce significant amounts of ashes, which are quite often being used as additives in cement and other building materials. In many cases, coal and lignite present high concentrations of naturally occurring radionuclides, such as 238U, 226Ra, 210Pb, 232Th and 40K. During the combustion process, the produced ashes are enriched in the above radionuclides. The different enrichment of the various radionuclides within a Radioactive series, such as that of 238U, results in the disturbance of Radioactive secular Equilibrium. An extensive research project for the determination of the natural radioactivity of lignite and ashes from Greek lignite-fired power plants is in progress in the Nuclear Engineering Department of the National Technical University of Athens (NED-NTUA) since 1983. This paper presents detailed results for the natural radioactivity, the secular Radioactive Equilibrium disturbance and the radon exhalation rate of the fly-ash collected at the different stages along the emission control system of a lignite-fired power plant as well as of the bottom-ash. From the results obtained so far, it may be concluded that 226Ra radioactivity of fly-ash in some cases exceeds 1 kBq kg−1, which is much higher than the mean 226Ra radioactivity of surface soils in Greece (25 Bq kg−1). Furthermore, the radioactivity of 210Pb in fly-ash may reach 4 kBq kg−1. These results are interpreted in relation to the physical properties of the investigated nuclides, the temperature in the flue-gas pathway, as well as the fly-ash grain size distribution. It is concluded that towards the coldest parts of the emission control system of the power plant, the radioactivity of some natural nuclides is gradually enhanced, secular Radioactive Equilibrium is significantly disturbed and the radon exhalation rate tends to increase.

  • determination of depleted uranium in environmental samples by gamma spectroscopic techniques
    Journal of Environmental Radioactivity, 2004
    Co-Authors: D J Karangelos, M.j. Anagnostakis, E P Hinis, S E Simopoulos, Zora S Zunic
    Abstract:

    sequently for the isotopic abundance of the uranium isotopes in the sample. 235U is determined from the analysis of the multiplet photopeak at 186 keV. DU may be detected with this technique provided that the 238U activity of the DU is higher than ~20% of that of 238 U in the natural uranium of the sample. The analyses by NES-NTUA of surface soil samples collected well before the dispersion of depleted uranium in Kosovo, made evident that Kosovo is an area of high natural background, with a pronounced surface soil variation in natural uranium content, and 238U activity reaching values as high as 330 Bqkg -1 . It was also observed that disturbance of Radioactive Equilibrium among the nuclides of the uranium series is quite often observed due to leaching and weathering, with the ratio of the activities of 238 U and 226 Ra ranging from 0.17 to 5.5. After the military operations in Kosovo, surface soil and vegetation samples as well as DU penetrators were analysed in NES-NTUA. Among the soil samples analysed it was found that some of those collected around a DU penetrator crater were contaminated by DU, with 238 U activity exceeding 2 kBqkg -1 , and ratio of 238 U/ 226 Ra exceeding the value of 10. In these soil samples, the natural isotopic abundance of the uranium isotopes was significantly disrupted; this allowed for an estimation of the isotopic abundance of 235U in the dispersed DU of about 0.2%, which agrees very well with relevant values found in the literature for DU penetrators. DU in the vegetation samples analysed was below detection limit. The analysis of DU penetrators led to the detection 238U, 235 U and their daughters, and to an estimation of the dose-rate due to the gamma-rays emitted from the penetrator, which reached 6.5 µSvh-1 on the surface, sloping to background at the distance of about 40 cm.

  • photon attenuation natural radioactivity content and radon exhalation rate of building materials
    Journal of Environmental Radioactivity, 2002
    Co-Authors: N P Petropoulos, M.j. Anagnostakis, S E Simopoulos
    Abstract:

    Abstract High concentrations of natural radionuclides in building materials can result in high dose rates indoors, from both internal and external exposure. In dose calculations, the main radionuclides of interest are 226 Ra, 232 Th and 40 K. Usually much attention is paid to 226 Ra due to 222 Rn exhalation and the subsequent internal exposure. Other radionuclides of the uranium series such as 238 U and 210 Pb, emitting low energy photons are not usually determined and an assumption of Radioactive Equilibrium is made. The above assumption is seldom checked mainly because of the difficulties in the γ-spectroscopic analysis of low energy photons. For the determination of radionuclides emitting low-energy photons, in samples like building materials where intense self-absorption of the photons exists, a method for self-absorption correction has been developed. The method needs as input the linear attenuation coefficient μ for the material under analysis. This paper presents: 1. Correlations in the form μ = f ( ρ , E ) developed for the estimation of the linear attenuation coefficient μ (cm −1 ), as a function of the material packing density ρ (g cm −3 ) and the photon energy E (keV), for building materials as well as other materials of environmental importance. 2. Gamma-spectroscopic analysis techniques used for the determination of 238 U, 226 Ra, 210 Pb, 232 Th and 40 K in environmental samples, together with the results obtained from the analysis of building materials used in Greece, and industrial by-products used for the production of building materials. Among the techniques used, one is based on the direct determination of 226 Ra and 235 U from the analysis of the multiplet photopeak at ∼186 keV. 3. Results from radon exhalation measurements of building materials such as cement and fly-ash and building structures conducted in the radon chambers in our Laboratory. Based on the above results, dosimetric calculations are also reported.

N. N. Zhukov - One of the best experts on this subject based on the ideXlab platform.

Morten B Andersen - One of the best experts on this subject based on the ideXlab platform.

  • experimental evidence for 234u 238u fractionation during granite weathering with implications for 234u 238u in natural waters
    Geochimica et Cosmochimica Acta, 2009
    Co-Authors: Morten B Andersen, Yigal Erel, Bernard Bourdon
    Abstract:

    Abstract The daughter to parent (234U/238U) activity ratio in natural waters is often out of secular Radioactive Equilibrium. The major reason for this disEquilibrium is related to the energetic α-decay of 238U and differential release of 234U relative to 238U. This disEquilibrium originates from (1) preferential release of more loosely bound 234U from damaged mineral lattice sites or; (2) direct recoil of 234Th into surrounding media from near mineral surface boundaries, however, it is unclear which of the two mechanisms is most important in nature. To better quantify the effects of preferential release of 234U, two continuous laboratory granite leaching experiments conducted over 1100 h were performed. The leachates were characterized by declining U concentrations with time and (234U/238U) initially greater than unity (up to 1.15), which changed to below unity during leaching (∼0.95). The early elevated (234U/238U) suggests that additional 234U is released into solution by preferential release of 234U from mineral phases. However, the excess 234U constitutes a finite pool of easy leachable 234U and the (234U/238U) values become lower than unity when this pool is used up. A model based on first-order kinetics, dissolution rates and preferential release of 234U from damaged lattice sites was developed and is able to quantitatively predict the observed pattern of (234U/238U) values and U concentrations for the two granite leaching experiments. Extending the modeling to longer time scales more comparable to natural systems shows that the production of waters with high (234U/238U) ratios can be achieved in two distinct regimes (1) slow weathering where the rate of directly recoiled 234U near mineral surfaces into waters is high; (2) fast weathering where the role of incipient chemical weathering and preferential release of loosely bound 234U are important. The model is able to explain apparent opposite correlations between physical erosion rates and (234U/238U) in waters and it provides a new framework that will be useful for examining weathering regimes, their timescales and their coupling with physical erosion.